This invention relates to a gasoline fuel system for an internal combustion engine using a down-draft carburetor having a booster venturi (also referred to as an "auxiliary venturi tube") above the throttle valve (throttle plate), and more particularly to the vaporization of gasoline as it issues from the fuel nozzle into the booster venturi within the carburetor.
A conventional fuel system for an internal combustion engine uses a carburetor in which gasoline is sprayed into a stream of air and divided into a profusion of fine droplets or "mist" which is conveyed to the cylinders of the engine where the gasoline is ignited. Though the gasoline is referred to as being "atomized" the droplets are relatively large in comparison with a molecule of gasoline, or a cluster of a few thousand molecules.
When a relatively large droplet is introduced into the cylinder, because of the very short time allowed for combustion, incomplete combustion results. This in turn leads to inefficient engine operation, and to the presence of large quantities of unburned hydrocarbons, carbon monoxide and nitrogen oxides in the exhaust, all to the detriment of the atmosphere.
If the gasoline can be heated sufficiently to behave according to the kinetic molecular theory of matter, gasoline with lower octane rating may be used than would otherwise be required with conventional carburetion. As is well recognized by those skilled in the art, the closer to a true gas the heated gasoline approaches, the more predictable is its volume-temperature-pressure behavior, and correct fuel to air ratios may be maintained in the mixture being ignited in the cylinders of an engine, for better efficiency.
The prior art is replete with attempts to improve vaporization of the gasoline, and include the use of compressed gases, the addition of water or steam under pressure, the use of fuel gas generators where the gasoline is vaporized prior to introduction into a carburetor, and numerous other systems, almost all of which have achieved a notable lack of success.
Examples of fuel gas generators are provided in U.S. Pat. Nos. 4,023,538; 4,050,419; 4,194,476; 4,213,433; and the numerous references cited therein. Illustrative of the advanced state of the art of providing a purely gaseous fuel mixture is the system disclosed in U.S. Pat. No. 3,872,191, which system, like most of the others are so complicated as to be either functionally impractical, or uneconomical, or both. In contrast the device of my invention is the essence of simplicity, yet provides the same functions as the complicated devices.
Exhaust recycle streams, that is, a slipstream taken from the exhaust of an engine and returned to the carburetor, have been used in a variety of different configurations, all with the purpose of improving efficiency and control of the fuel combustion process. For example, U.S. Pat. No. 2,317,582 to G. M. Bicknell discloses an exhaust slipstream recycled to the carburetor above the throttle plate, just below the nozzle through which fuel is injected into the venturi, and he found it necessary to connect the intake and exhaust manifolds of the engine. As will be immediately evident, the valving of the slipstream leads to undue complications, and additionally, the teachings of this reference failed to grasp the significance of the precise location for introducing the slipstream if one is to obtain optimum efficiency without sacrificing the quality of the exhaust emissions.
The shortcomings of the Bicknell system were recognized in U.S. Pat. No. 2,589,536 to M. C. Carbonaro who took an exhaust slipstream and supplied it to a venturi constituting a secondary by-pass which was used in addition to a primary by-pass. The primary by-pass connected a venturi to the lower portion of the body of the carburetor below the throttle plate. Though the valving of the slipstream was avoided, it required that the attenuated velocity of the slipstream be used to provide the forced atomization he sought, and the slipstream did not directly heat the fuel nozzle to accelerate vaporization of the fuel sprayed from it.
Moreover, the '536 patent failed to recognize that an unattenuated slipstream directly into the carburetor would provide a conduit for sparks from the engine and ignite the fuel in the carburetor.
Further, the use of recycled exhaust slipstreams about two decades ago was given scant attention in the subsequent years because of the problems with exhaust emissions. At the present time, a slipstream from the exhaust gases is recycled to an exhaust gas recycle port in the main body of several types of down-draft carburetors but its function is not to heat the booster venturi and the gasoline discharged into and from the booster venturi. Typically, an exhaust gas recycle (E.G.R.) is provided to control emissions by introducing a metered amount of exhaust gas into the carburetor, below the throttle plate, with suitable valving, as for example in the Carter RBS carburetor. The E.G.R. port connects to the primary bore and allows the metered amount of exhaust gas to be fed into the fuel-air mixture. This exhaust emission control system is presently used, most of them with unleaded gasoline, in combination with catalytic mufflers, air pumps, PCV valves, and the like. The present invention may be used in conjunction with any currently used emission control system, including one in which the carburetor has an E.G.R. port, without deleteriously affecting the system's performance. In other words, the present invention is designed for use with a down-draft carburetor fed with a float-controlled gasoline supply, without in any way modifying the emission control system presently used on the internal combustion engine.